What is in this article?:
- Finding solutions to Bagrada bug control in the West
- Insecticide control
- Slow damage rate
- University of Arizona research on the Bagrada bug is now yielding answers to help farmers and pest control advisers better understand and control the pest.
- Bagrada bug adults and nymphs feed on young cole crop plants including broccoli, cauliflower, cabbage, brussel sprouts, kale, turnip, mustard, and radish.
- The insect’s needle-like stylet mouthpart sucks the sap from leaves - essentially killing or maiming cotyledons and growing points.
Bagrada bugs and a damaged broccoli seedling.
“Research to date also suggests that heavy Bagrada bug infestation control with insecticides is the most economically viable option to protecting stands and preventing significant yield losses,” Palumbo said.
This includes chemigation with pyrethroids, and using contact insecticides (pyrethroids, Lannate, Lorsban) once plants emerge and the irrigation pipe is pulled.
After stands are established and plant size increases up to the 3-4 leaf stage, or on growing transplants, PCAs may consider alternating to dinotefuron (Venom/Scorpion) to protect plants from Bagrada feeding. This neonicotinoid also provides knockdown of whitefly adults and nymphs.
Part of Palumbo’s research strategy is to better understand the Bagrada bug’s feeding behavior.
“The bottom line is the Bagrada bug in the feeding mode tears up the leaf tissue,” Palumbo said.
Many stink bugs, including the Bagrada, use a ‘lacerate and flush’ feeding method. The stylet, about half the length of the insect’s body, pierces the leaves and sucks out the juice.
In a laboratory tests, Palumbo placed a four-to-five-day-old broccoli cotyledon in a plastic tub and placed a single Bagrada bug on the leaf. Another plastic tub was placed on top to keep the insect from escaping. It was the perfect feeding opportunity for the hungry insect.
UA research specialist Marco Pena harnessed a microscope, video camera, and time-lapse photography to record the feeding activity. A UA-produced video features the process. Palumbo showed and narrated the video during his workshop presentation.
“The Bagrada bug finds a point in the leaf and then the stylet comes in and destroys the leaf cells on the top of the leaf surface,” Palumbo said. “Look here,” Palumbo shouted. “We suspect the insect is depositing salivary enzymes in the leaf - not a virus or a feeding toxin - to help break down the cellular tissue.”
Initial feeding creates starburst-shaped lesions on the leaves and circular scorched areas as the plant cells die.
“This rapid feeding means the grower cannot afford to have the insect feed very long or else the plant will be stunted or killed,” Palumbo said.
Pena’s video was shot over a two-and-a-half-day period and was edited down to several minutes to showcase the feeding frenzy.
After the first one-half hour, the bug had tagged the first cotyledon. At six hours, the insect consumed a good portion of the cotyledon. At 12 hours, the cotyledons began to wilt. The first cotyledon was dead at 18 hours. The insect often fed from the bottom of the cotyledon leaf to the top side.
Next, the insect fed on the main terminal - the apical meristem – the plant part that, for example, produces a cauliflower or broccoli head.
“For growers, that’s where the money is made or lost,” Palumbo said.
At 60 hours (two and a half days), the plant was basically destroyed.
“Both cotyledons are essentially desiccated. The terminal is pretty messed up,” Palumbo said. “This is why we see a lot of blind plants with no heads, particularly at the cotyledon stage for seedling plants at stand establishment. This illustrates how active this insect can be under ideal conditions.”